1. Field of the Invention
This invention relates to a damper and, more particularly, to a damper suitably used as a shock absorber provided on a suspension of a vehicle.
2. Description of the Prior Art
A shock absorber utilizing inertia and tending to hold a damping force small when high frequency vibrations are input from a tire while tending to increase the damping force when low frequency vibrations are input from the tire has been proposed (Japanese Utility Model Public Disclosure (KOKAI) No. 62-43805). This shock absorber includes a partition member for partitioning the interior of a cylinder into two liquid chambers, a path provided in the partition member and affording communication between both liquid chambers, an auxiliary liquid chamber formed in an intermediate portion of the path, and a valve body serving as a mass body and vertically movably disposed in the auxiliary liquid chamber.
The valve body is provided on a shoulder with an orifice and a damping force is generated by liquid flowing through the orifice. When a relative displacement takes place between the partition member and the valve body, the flow area of the orifice is varied. Thus, the magnitude of the damping force is adjustable.
Another damping device utilizing inertia has also been proposed (Japanese Utility Model Publication No. 43-17469). According to this damping device, a bypass path provided in a piston rod affords communication between two liquid chambers, which are partitioned by a piston, inside a cylinder, while a mass body is movably disposed in an opening end of the bypass path.
When a relative displacement takes place between the piston rod and the mass body, the flow area of the mass body communicating to the bypass path is varied to vary the quantity of liquid flowing in the bypass path.
In the shock absorber disclosed in the former Public Disclosure, since the valve body moves vertically in the auxiliary liquid chamber, an internal path of a small bore is provided in the valve body itself in order to ensure the movement of the valve body. Thus, when the relative displacement takes place between the valve body and the partition member, liquid passes through the internal path to generate a delay in the movement of the valve body due to the resistance at the time of passage of the liquid. This is only because the function of changing the damping force is not sufficiently fulfilled particularly when the high frequency vibrations are input.
In the damping device disclosed in the latter publication, the mass body moves under the condition that the mass body substantially receives no resistance. Accordingly, the mass body sufficiently relatively moves to vary immediately the area of the bypass path when an external force is exerted to bring about the relative displacement between the piston rod and the mass body. However, since the mass body biased toward the neutral position by the action of a coiled spring, the mass body is moved quickly in a direction of hindering the variation of the area of the bypass path by the action of the coiled spring. This means that the change-over of the damping force frequently occurs to bring about the generation of an impact force.